The conventional injection molding process for making complex plastic parts or components has been around for over six decades. The modern investment casting process, also known as precision casting, which leverages injection molding technology for making wax patterns and ceramic cores for making complex metal parts, such as for the aerospace and defense industries, has been around for almost as long. Powder injection molding (PIM) is a process in which a metal or ceramic powder/binder mixture is injection molded, and after binder removal and sintering, a net shape part is produced. The PIM technology again leverages existing molding technology. However, all of these processes are still limited in providing capabilities to produce complex three dimensional (3D) parts.
Conventional injection molding, investment casting, and PIM are limited to 2½D geometries due to tooling constraints, such as parting line and draft angle. The parting line defines the opening of the two-piece mold, where the linear motion of the mold halves during opening restricts the dimensionality of the molded part. The part can be three dimensional, but no portion of the part can be in front of any other section of the part in the mold opening direction, where it interferes with the mold opening process. Draft angles are tapers on the part surfaces that allow the part to slide past the mold walls as the part is being ejected. A complex three dimensional (3D) part as described in this disclosure relates to three dimensional parts not limited by such tooling constraints.
The tooling constraints not only limit manufacturability, but further limit the design process, becoming design constraints. Design engineers need to constantly consider tooling constraints, such as the parting line and draft angle requirements, during the design process. Such consideration hinders the creativity of the designer, which can affect the design and performance of the final product. Design constraints are illustrated in the design of internal cooling technology for heat transfer and external aerodynamic surfaces for minimizing flow resistance in the aerospace, airframe and aircraft engine industries. Removal of the design restrictions on three dimensional internal cooling pathways and external three dimensional shapes would enable better product performance and faster design process.
The time for tooling design and fabrication is also significant, as it may span several months for complex parts. The cost of hard tooling also becomes very high for components with complex geometries. Multiple iterations of tool modifications are frequently needed to adjust the tools for the necessary tolerances, making these processes impractical, especially for low volume or one-of-a-kind applications.
Although injection molding mechanisms such as side-actions or cam-actuated slides exist to fabricate 3D geometries, these techniques are generally restricted to a few specific 3D geometries. The tooling development for such techniques is also very expensive, and requires a long turnaround time. As a result, these approaches are extremely costly and are generally not applicable for limited quantity part production.
Rapid Prototyping (RP) techniques bypass the 2½D tooling constraint. Rapid Prototyping refers to a group of technologies developed with the goal of shortening the design and development cycles. With these techniques, complex 3D parts can be made in much less time, often only a matter of days, without the need for tooling, setup and assembly. However, such 3D parts may have limitations with respect to the material performance and the manufacturing speed for parts composed of high temperature materials such as metals or ceramics. As an illustration, metallic or ceramic 3D parts produced by conventional layer manufacturing techniques may be subject to delamination due to weak bonding between the layers. As a result, parts produced by layer manufacturing are generally used as prototypes, not as production parts, as they are generally not suitable to withstand the loading conditions typical in real-world applications. In an alternative illustration, metallic or ceramic 3D parts produced by high-power point-source layer manufacturing techniques are characterized by slow production speed.